Journalist Jamal Khashoggi was strangled to death soon after entering the Saudi consulate in Istanbul, while his body was "cut into pieces", chief Turkish prosecutor Ifran Fidan said.
Turkish President Recep Tayyip Erdogan said the investigation needs to be completed swiftly.
Noting that forensic examination, including an autopsy on the victim's body is crucial in any murder investigation, Bachelet urged the Saudi authorities to reveal the whereabouts of Khashoggi's body "without further delay or prevarication".
"No reservations at all".
Turkey is seeking the extradition of 18 Saudi suspects detained in Saudi Arabia over the killing of Mr Khashoggi.
The Turkish investigators rejected the request, TRT said, instead calling on the Saudi prosecutor to reveal information about the location of Khashoggi's body, which has not yet been found.
After weeks of denials, Riyadh has sought to draw a line under the crisis with an investigation.
The statement comes after Saudi Arabia's chief prosecutor, Saud al-Mojeb, left Turkey following meetings with his counterpart in Istanbul.
"The Saudis know the answers to both those questions, and Mr. Trump might, too".
Addressing a forum in Manama on Saturday, Mattis warned that "the murder of Jamal Khashoggi in a diplomatic facility must concern us all greatly".
Prince Ahmed bin Abdelaziz, the youngest and only living brother of King Salman, has reportedly returned to the kingdom from London this week.
The board said that Congress should summon CIA Director Gina Haspel, who was in Turkey last week and briefed Trump, and other senior US officials and determine what they know about the killing.
The kingdom initially said it knew nothing about what happened to Khashoggi, but on Thursday said evidence shows the killing was premeditated.
Khashoggi, who lived in exile, had written critically of Saudi Arabia's crown prince.
The fiancee of slain journalist Jamal Khashoggi has called on U.S. President Donald Trump and other leaders to ensure that his killing at the Saudi Consulate in Istanbul is not covered up.
Saudi reluctance to cooperate, as well as the USA investigation and Ms. Cengiz's possible meeting with Trump, complicate apparent Turkish efforts to find a resolution of the escalating crisis that would allow Saudi Arabia to save face and salvage Turkey's economic relationship with the kingdom.
The U.S. -Saudi relationship "is too big to fail", Turki said.
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